OPINION
PER CURIAM.
These cases arise out of the refusal of Cool Homes, Inc. (Cool Homes) to pay prop[1252]*1252erty taxes assessed against it by the Fairbanks North Star Borough (Borough). The appeals raise the following separate issues.
The issue in No. S-3995 is whether the superior court erred in granting summary judgment against Cool Homes in the Borough’s action to foreclose Cool Homes’ interest in its buildings on Eielson Air Force Base. The court ordered the buildings sold and transferred to the Borough for the amount of taxes, penalties, interest, advertising costs and legal fees for which the property is liable.
No. S-4337 arises out of an action by the Borough for a personal judgment against Cool Homes. The Borough sought the personal judgment to recover the property taxes assessed against Cool Homes' leasehold interest in the land, including statutory penalties and interest. The superior court granted summary judgment in favor of the Borough. The issue thus is whether Cool Homes may be held personally liable under the assessment and foreclosure statutes.
Nos. S-4338-4353 raise several discrete issues concerning the reassessment of the Cool Homes’ properties, including whether the Borough violated the Open Meetings Act during the reassessment process, the relative burdens on the taxing authority and the property owner, adjustments for lease restrictions and whether the superior court abused its discretion in permitting supplementation of the record on appeal.
I. FACTUAL AND PROCEDURAL BACKGROUND
The backdrop for these appeals is set forth generally in Ben Lomond, Inc. v. Fairbanks North Star Borough Board of Equalization, 760 P.2d 508 (Alaska 1988). Cool Homes, the successor in interest to Ben Lomond, Inc. (Ben Lomond), owns approximately three hundred units of housing on Eielson Air Force Base. Ben Lomond constructed these houses on land leased in 1985 from the federal government. This Land Lease runs for twenty-three years and provides for a nominal lease rental. The federal government, in turn, leased the housing development and underlying land from Ben Lomond for an annual lease rental of $3,600,000.00 plus an annual maintenance fee. The term of this “Project Lease” is twenty years, running concurrently with the last twenty years of the Land Lease.
The Land Lease is authorized under 10 U.S.C. § 2667, which provides:
(a) Whenever the Secretary of a military department considers it advantageous to the United States, he may lease to such lessee and upon such terms as he considers will promote the national defense or be in the public interest, real or personal property that is
(1) under the control of that department;
(2) not for the time needed for public use; and
(3) not excess property, as defined by section 3 of the Federal Property and Administrative Services Act of 1949 (40 U.S.C. 472).
(e) The interest of a lessee of property leased under this section' may be taxed by State or local governments. A lease under this section shall provide that, if and to the extent that the leased property is later made taxable by State or local governments under an Act of Congress, the lease shall be renegotiated.
The Project Lease is authorized under the Military Construction Authorization Act of 1984 (Act), Section 801, codified as 10 U.S.C. § 2828. The Act inaugurated a test program “to determine if leasing is more cost effective to the [United States] than the traditional method of constructing [military] ■ housing with appropriated funds.” While the Act does not refer specifically to taxation, there is no indication that 10 U.S.C. § 2828 was intended to supersede 10 U.S.C. § 2667, which provides for taxation of private interests.
[1253]*1253The terms of the lease between the federal government and Ben Lomond specifically address Ben Lomond’s responsibility for taxes assessed against the property. Condition 13 of the Land Lease provides:
That the Lessee [Cool Homes] shall pay to the property authority, when and as the same become due and payable, all taxes, assessments, and similar charges which, at any time during the terms of this lease, may be taxed, assessed, or imposed, upon the Lessee’s interest in the leased premises. In the event any taxes, assessments, or similar charges are imposed, with the consent of Congress upon property owned by the Government and included under this lease (as opposed to the leasehold interest of the Lessee therein), they shall be paid (1) by the Government, in which event this lease shall then be renegotiated to increase the consideration provided above in the amount of such taxes, assessments, or similar charges paid by the United States, or (2) at the option of the Government, by the Lessee.
Article VII of the Project Lease provides, in pertinent part:
Lessor [Cool Homes] shall pay all taxes, general or special, all public rates, dues, and special assessments of every kind which shall become due and payable or which are to be assessed against or may be levied upon said Premises during the terms of this Lease.
The Borough assessed the property for the years 1986, 1987 and 1988. Although the Borough mailed property tax bills to Cool Homes for each of these years, the corporation has paid no part of the property taxes. Pursuant to AS 29.45.210(d), Cool Homes sought judicial review of each assessment. The superior court upheld the Borough’s right to tax Cool Homes’ interest, but remanded all of the assessments to the Borough Board of Equalization (Board) for recalculation of the amount based on a twenty-three year lease, rather than on a forty-year lease.
In affirming Cool Homes’ obligation to pay property taxes, we held that “Lo-mond’s [now Cool Home’s] twenty-three year leasehold interest in land at Eielson Air Force Base and its twenty year interest in the improvements it constructed upon the land are both taxable interests under the Borough’s real property taxation statutes.” Ben Lomond, 760 P.2d at 513.
The exact amount Cool Homes owed was still in dispute following our decision. The Board reassessed the property in May 1989. The superior court affirmed these assessments. Cool Homes, Inc. v. Fairbanks Northstar Borough Board of Equalization, No. 4FA-89-1078 Civ. (Alaska Super., November 19, 1990). This proceeding was a consolidated appeal of the 1986-89 assessments. Cool Homes appealed. See Nos. S-4338, 4353.
The Borough also filed an action for a personal judgment against Cool Homes. The superior court granted the Borough summary judgment in that case as well. Fairbanks Northstar Borough v. Cool Homes, Inc., No. 4FA-89-1415 Civ. (Alaska Super., November 19, 1990). Cool Homes appealed. See No. S-4337.
Prior to the superior court’s decision in the reassessment proceeding, the Borough filed a petition for judgment of foreclosure against Cool Homes. The petition was part of the Borough’s annual general in rem foreclosure action. The Borough submitted its delinquent tax foreclosure list and published the list for four consecutive weeks in a newspaper of general circulation. Cool Homes filed an answer and objection to the foreclosure action. Pursuant to AS 29.45.390(a), the court separated Cool Homes’ property from the in rem proceeding and dealt with it separately. The Borough filed a Motion for Summary Judgment as to Cool Homes. Following briefing and oral argument, the court granted the Borough’s Motion for Summary Judgment and ordered Cool Homes’ interest foreclosed. Cool Homes appealed. See No. 3995.
[1254]*1254II. DISCUSSION
A. No. S-3995
1. STANDARD OF REVIEW
“When reviewing a grant of summary judgment, this court must determine whether there was a genuine issue of material fact and whether the moving party was entitled to judgment on the law applicable to the established facts.” Merdes v. Underwood, 742 P.2d 245, 248 (Alaska 1987) (quoting Zeman v. Lufthansa German Airlines, 699 P.2d 1274, 1280 (Alaska 1985)). The court considers matters of law de novo and adopts rules of law which are most persuasive in light of precedent, reason and policy. Guin v. Ha, 591 P.2d 1281, 1284 n. 6 (Alaska 1979).
2. THE BOROUGH’S MOTION FOR SUMMARY JUDGMENT
a. Cool Homes Has a Property Interest Subject to Foreclosure.
Cool Homes distinguishes its two interests that have been taxed. First, it has a leasehold interest in the land upon which it constructed military housing.1 Second, it has an ownership interest in the buildings it constructed. Cool Homes argues that the buildings cannot be considered real property absent any connection to the land. According to Cool Homes, its interest in the buildings is not subject to real property taxes since the federal government owns the underlying land. Cool Homes concedes that the buildings are taxable as personal property, but maintains that they are not subject to foreclosure.
The Borough asserts that governments traditionally enforce liens on taxable interests in tax-exempt property. It cites cases from other jurisdictions in support of the position that it may foreclose upon the ownership interest in the improvements, notwithstanding the location of the buildings on tax-exempt federal property. The Borough argues that such separation of property interests for tax purposes is permitted under article IX, section 4 of the Alaska Constitution.2
We agree with the Borough. In Ben Lomond, 760 P.2d at 513, we stated that Ben Lomond’s [now Cool Homes’] “interest in the improvements it constructed upon the land [is taxable] under the Borough’s real property taxation statutes.” Id. (emphasis added). Cool Homes’ argument that the buildings are personal property because the corporation does not own the underlying land ignores the court’s previous explicit holding that the improvements are real property.3
Cool Homes’ argument that the Borough cannot foreclose on the buildings to collect delinquent taxes is also without merit. Ownership of property consists of a bundle of separate rights, powers and privileges. See e.g., Wm. E. Burby, Handbook on the Law of Real Property § 9, at 13-14 (3rd ed. 1965). Although Cool Homes does not own the underlying land, it owns the buildings it constructed on Eielson Air Force Base.
There appears to be no insurmountable difficulty in foreclosing on the houses without foreclosing on the land. This was the situation in Brown v. Hart, 213 Mont. 517, 692 P.2d 14 (1984), where the court upheld [1255]*1255the tax sale of a privately owned cabin on federal land. In Brown, the court stated:
The cabin in question is located on Forest Service land on Seeley Lake. It was built more than twenty years ago and, although it lacks a foundation, is “affixed” to the land by means of water and sewer lines. No hair-splitting distinctions are, however, required. The cabin, so long as it remains upon the land, is real property.... An objective test applies: the taxing authority need only observe the structure; the present or future intentions of the parties are irrelevant. The cabin is a building resting on the land. The fact that it may be moved or may have to be removed in the future does not, for tax and recording purposes, change the nature of the cabin as real property.
692 P.2d at 15-16. See also First National Bank of Beresford, South Dakota v. Anderson, 332 N.W.2d 723, 726 (S.D.1983) (holding that real estate can be severed to preserve a homestead exemption and the non-exempt remainder ordered sold to satisfy a civil money judgment).
Brown is not distinguishable simply because Cool Homes’ interest is non-posses-sory. The non-possessory nature of Cool Homes’ interest precludes neither taxation nor foreclosure.4
The federal government is in a position similar to that of a tenant whose landlord has failed to pay property taxes. The tenant cannot prevent foreclosure by the taxing authority, just as the tenant cannot prevent foreclosure by a private creditor if the landlord fails to make mortgage payments.5
b. Cool Homes’ Appeal of its Tax Assessment and the Superior Court’s Remand for Reassessment Precludes Foreclosure.
Cool Homes argues that no valid tax assessment existed until May 22, 1989, when the Board of Equalization reassessed the property following remand of the 1986-88 assessments to it by the superior court. Since Alaska statutes provide that an annual foreclosure list must be based on the previous year’s assessment, AS 29.45.330, Cool Homes argues that foreclosure on the 1989 assessment could not occur until 1990. Cool Homes also argues that interest and penalties could not begin to accrue against the corporation until May 22, 1989, when a valid assessment was made.
The Borough argues that Alaska statutes require a landowner to pay the taxes assessed and then sue for a refund if the' taxpayer believes the assessment is erroneous. According to the Borough, Cool [1256]*1256Homes could have avoided the interest and penalties as well as foreclosure, by paying the taxes assessed against it. The Borough also asserts that Cool Homes could have stayed execution of the tax assessment pending appeal by posting bond. Since Cool Homes has failed to pay any of its property taxes and failed to post bond to stay execution of tax enforcement, the Borough argues that it is entitled to foreclose on Cool Homes’ buildings.
Alaska statutes provide aggrieved taxpayers with a number of remedies. The taxpayer may pay taxes under protest and then sue for a refund. If the taxpayer is entitled to a refund, he or she receives interest and costs, in addition to the amount of taxes that had been collected in error. AS 29.45.500(a).6 In addition, a taxpayer can obtain a stay of the tax execution pending appeals to the superior and supreme courts by posting bond. City of Nome v. Catholic Bishop of Northern Alaska, 707 P.2d 870, 878 (Alaska 1985). Alaska R.App.P. 204, 603.
However, in the case before us the taxpayer has proceeded beyond the appeal stage. The taxpayer has obtained a reversal of the action of the Board and vacation of the assessment, and the matter has been remanded to the Board to rectify its errors.7
We summarily rejected8 the Borough’s argument that it may proceed with foreclosure notwithstanding the superior court’s remand to the Board of Equalization for reassessment.9 Since the amount of the tax due had not been determined when the Borough initiated foreclosure, the amount of its lien had not been established. Interest and penalties could not be determined, since there was no figure on which to base them. The taxpayer’s right of redemption was impaired, because the taxpayer could not ascertain what amount it had to pay to avail itself of the right.10
c. Penalties and Interest.
In calculating the tax obligations on remand the superior court must decide whether late payment penalties and interest on the tax lien are appropriate. We thus address the issue of whether interest and penalties should run from the original [1257]*1257due date for each tax year or only from the date of reassessment after remand.11
The superior court ordered foreclosure on a tax lien which included statutory penalties and interest, dating back to 1986, 1987 and 1988. Cool Homes contends that this is improper because the tax assessment after remand was not made until May 1989. The Borough argues that the interest and penalties may be properly dated back to the original due date as distinguished from the actual date of assessment following an appeal.
Alaska statutes allow a municipality ’ to add a penalty to all “delinquent” taxes and provide that interest may accrue “from the due date.” AS 29.45.250. Interest and penalties serve different functions and thus separate standards are appropriate. Penalties are meant to punish a party for late payment. Interest, however, is not punitive.12 Rather, it is intended to compensate the party to whom the sum is owed for the use of the money during the period of nonpayment. Lundgren v. Gaudiane, 782 P.2d 285, 289 (Alaska 1989).13 Neither prejudgment nor postjudgment interest depends on which party is at fault for the delay. Farnsworth v. Steiner, 638 P.2d 181, 184-85 (Alaska 1981).
We have previously held that for the purposes of former AS 29.53.180, the precursor to AS 29.45.250,14 there can be no delinquency until a “valid” tax is assessed. Alascom, Inc. v. North Slope Borough, Bd. of Equalization, 659 P.2d 1175, 1180 (Alaska 1983). In Alascom, the municipality failed to list certain real property on its tax rolls and the property therefore “escaped” taxation. Instead the property was assessed in 1979 for the six prior years. Id. at 1177. We held that interest and penalties were not authorized because of the municipality’s failure to discharge its responsibility as to real property to timely assess the property and notify the taxpayer. We stated:
As to real property the responsibility for assessing taxable parcels and for notifying a taxpayer of his tax liability rests solely with the borough. As we have previously ruled, a tax on real property is ineffective until the borough discharges its responsibilities by making an assessment, notifying the taxpayer of his liability, and providing the taxpayer with an opportunity to pay his taxes. Until the borough has exercised its right to demand real property taxes in the manner provided by statute there can be no valid tax and hence no delinquency within the meaning of AS 29.53.180, which authorizes penalties and interest on delinquent taxes.
Alascom, 659 P.2d at 1180 (footnote omitted). This rationale is not applicable where the municipality makes an assessment of the real property in question, but makes a mistake as to the amount of the assessment. In such a case the property owner is aware that taxes are being demanded and [1258]*1258can pay them immediately under protest, AS 29.45.500, or it can take an administrative appeal to the Board of Equalization, AS 29.45.190, and to the superior court, AS 29.45.200. The taxpayer whose property is timely assessed should be aware that in all likelihood its property will generate some tax liability and can plan for that eventuality. Alascom does not stand for the proposition that interest on taxes imposed on property which is timely assessed should not relate back to the original due date.
However, we view Alascom as authority with respect to penalties. Although the question is a close one and the applicable statute, AS 29.45.250, gives no guidance, it seems appropriate to require an error free assessment before penalties can be imposed. Thus, in this case, penalties may be charged only from the due date which follows May 22, 1989. The superior court erred in charging Cool Homes penalties which dated back to 1986, 1987 and 1988.
With respect to interest, the “due date” refers to when the cause of action arises and not when a judgement is awarded. “When a cause of action arises, the injured party become immediately entitled to be made whole, and the amount later adjudicated as damages becomes due.” Farnsworth, 638 P.2d at 183. Thus the interest on a tax assessment runs from the due date in the year of the original assessment rather than from the date of reassessment.
B. No. S-4337
THE PERSONAL ACTION AGAINST COOL HOMES
The Borough filed a personal action against Cool Homes to recover the taxes assessed on Cool Homes’ leasehold interest in the land on Eielson Air Force base. The superior court granted summary judgment in favor of the Borough. Fairbanks North Star Borough v. Cool Homes, Inc., Case No. 4FA-89-1415 Civil (Sup.Ct. Nov. 19, 1990). Cool Homes contends that summary judgment was inappropriate because genuine issues of material fact exist and because the superior court improperly applied the law.
a. Standard of Review.
When reviewing a grant of summary judgment, this court must determine whether a genuine issue of material fact exists and whether the moving party is entitled to judgment as a matter of law. Merdes v. Underwood, 742 P.2d 245, 248 (Alaska 1887).15
b. Propriety of a Personal Action.
Cool Homes asserts that summary judgment is improper because the foreclosure action alone compensates the Borough for all unpaid taxes. It contends that the superior court erred as a matter of law in its interpretation of AS 29.45.320.
Alaska Statute 29.45.320(b) authorizes a personal action against the delinquent taxpayer if a tax assessed on a taxable interest in tax-exempt property is not paid.16 Cool Homes claims that this means only that a tax delinquency on an interest in real property which is not foreclosable may be remedied through a personal action. Cool Homes concludes that a taxing authority may institute a personal action [1259]*1259only if the property is not subject to foreclosure. We disagree.
Alaska Statute 29.45.320(b) authorizes a personal action to collect a delinquent tax assessed on a taxable interest in tax-exempt property. Cool Homes’s taxable interest is its leasehold interest in real property owned by the United States, which is tax-exempt property. Cool Homes’ unpaid tax is subject to a personal action.
Cool Homes also contends that the possible overlapping of a foreclosable interest and an interest subject to the personal judgment creates a genuine issue of material fact. We disagree.
Alaska Statute 29.45.320(b) specifically states that the personal action remedy is available “in addition to other remedies available to enforce the lien.” Foreclosure is another remedy available to enforce the lien and the personal action may be pursued in addition to foreclosure.17
C. Nos. S-4338/4353
Cool Homes appeals affirmance of the property taxes assessed by the Borough and seeks remand to the Borough’s Board of Equalization for redetermination. The Board cross-appeals, claiming that the superior court, on intermediate review, improperly supplemented the record.
1. THE BOARD DID NOT VIOLATE THE OPEN MEETINGS ACT
Whether or not the Board complied with the Open Meetings Act, AS 44.62.310, is a question of law. This court may substitute its judgment for that of the superior court. Ben Lomond, Inc. v. Fairbanks North Star Borough, Bd. of Equalization, 760 P.2d 508, 511 (Alaska 1988).
b. The Board’s Executive Session Was Not Improper.
On May 3, 1989, the Board convened to review the Borough’s assessment of Cool Homes’ property. Its first order of business was to call an executive session to discuss “the ins and outs and status of both Cool Homes and the Alaska Housing cases” and “litigation.” 18 Mark Andrews, [1260]*1260who served as both the Board’s and the Borough’s attorney, was present at the session. The session was held over Cool Homes’ objection.19
Cool Homes contends that this executive session was in violation of the Open Meetings Act, AS 44.62.310.20 Cool Homes thus asks that the Board’s actions be rendered void.
The Open Meetings Act requires that all meetings of any administrative board be open to the public. The act allows for certain excepted subjects to be discussed at executive sessions closed to the public. Among those excepted subjects are “matters which by law, municipal charter, or ordinance are required to be confidential.” AS 44.62.310(c)(3). The remedy provided by the Act is to void all action taken contrary to the Act. AS 44.62.310(f).
The superior court found that the Act was not violated because the executive session with the Board’s attorney was a protected communication. The court held that “[bjecause the attorney-client privilege operates concurrently with AS 44.62.310 although it is not an expressed exception, the Board’s executive session, called to discuss the status of this case with its attorney, did not violate AS 44.62.310.”
The Board claims that it is proper to assert the privilege in this case because the Board members had been threatened with personal liability if they failed to follow the directions given by the courts in the numerous appeals which preceded the hearing. Just three months before the hearing, Superior Court Judge Richard D. Saveli specifically suggested that Mr. Andrews, in his capacity as the Board’s counsel, advise the Board that any appearance of noncompliance with previous orders could potentially expose them to personal financial liability.21 Thus, the executive session was merely to allow the Board members to receive legal advice to protect themselves from personal liability.
The lawyer-client privilege is set out in Evidence Rule 503: “A client has a privilege to refuse to disclose and to pre[1261]*1261vent any other person from disclosing confidential communications made for the purpose of facilitating the rendition of professional legal services to the client ... between himself ... and his lawyer.” Alaska R.Evid. 503(b). A “client” includes an “organization or entity, either public or private.” Alaska R.Evid. 503(a)(1). Thus, the Board may exercise the privilege.22
The threshold question is thus whether the Open Meetings Act and the lawyer-client privilege can coexist. Cool Homes argues that they can, but not in this situation. We disagree.
The policies underlying the principle of open meetings are set out in AS 44.62.312. Among these is that “the people’s right to remain informed shall be protected so that they may retain control over the instruments they have created.” AS 44.62.312(a)(5). Thus, the applicability of the lawyer-client privilege must be narrow to afford this objective maximum realization. In The Sacramento Newspaper Guild v. Sacramento County Board of Supervisors, 263 Cal.App.2d 41, 58, 69 Cal. Rptr. 480 (1968) (since superseded by statute), relied upon by the superior court below, the California Court of Appeals noted the importance of limiting the privilege:
The two enactments are capable of concurrent operation if the lawyer-client privilege is not overblown beyond its true dimensions.... Public board members, sworn to uphold the law, may not arbitrarily or unnecessarily inflate confidentiality for the purpose of deflating the spread of the public meeting law. Neither the attorney’s presence nor the happenstance of some kind of lawsuit may serve as the pretext for secret consultations whose revelation will not injure the public interest.
Other jurisdictions have limited a lawyer-public body exception to their open meeting acts to consideration of pending litigation. Such a limitation reflects a concern that when the public body is a party to a lawsuit, it should not be disadvantaged by allowing its opponents access to its meetings with counsel. Smith County Educ. Ass’n v. Anderson, 676 S.W.2d 328, 334 (Tenn.1984) (would impair the attorney’s ability to fulfill ethical duties as an adjunct of the court); Oklahoma Ass’n of Mun. Attorneys v. State, 577 P.2d 1310, 1315 (Okla.1978) (might seriously impair the ability of the public body to process a claim or conduct pending litigation); Channel 10, Inc. v. Independent School Dist. No. 709, St. Louis County, 298 Minn. 306, 215 N.W.2d 814, 825-26 (1974) (the machinery of justice would be adversely affected if clients were not free to discuss legal matters with their attorneys without fear of disclosure).23 The exception is not appropriate for “the mere request for general [1262]*1262legal advice or opinion by a public body in its capacity as a public agency.” Minneapolis Star & Tribune Co. v. The Housing & Redevelopment Authority in and for Minneapolis, 246 N.W.2d 448, 454 (Minn. 1976).
The privilege should not be applied blindly. Id. at 453. It is not enough that the public body be involved in litigation. Rather, the rationale for the confidentiality of the specific communication at issue must be one which the confidentiality doctrine seeks to protect: candid discussion of the facts and litigation strategies. Channel 10, 215 N.W.2d at 825-26. See also City of San Antonio v. Aguilar, 670 S.W.2d 681, 686 (Tex.App.1984) (holding that a conference on decision to appeal deserves confidentiality); Hui Malama Aina O Ko’olau v. Pacarro, 4 Haw.App. 304, 666 P.2d 177, 183-84 (1983) (holding that a settlement conference deserves confidentiality). The principles of confidentiality in the lawyer-public body relationship should not prevail over the principles of open meetings unless there is some recognized purpose in keeping the meeting confidential. Channel 10, 215 N.W.2d at 825.
The privilege thus should be applied only when the revelation of the communication will injure the public interest or there is some other recognized purpose in keeping the communication confidential. Such requirements are especially appropriate where, as here, the public body’s counsel is also appearing before the body as an advocate. Public revelation of public counsel’s interpretation of “what has happened in the year between the last session and today as to Court findings” would not be injurious to the public interest. It might be informative and desirable.
However, we find this case to be a very specific exception to the Open Meetings Act. The Board members had been threatened with personal liability. The liability was with reference to ongoing litigation. By calling the executive session, the Board was merely following through on Judge Saveli’s admonition to the Borough’s counsel. The Board was entitled to legal advice as to how it and its members could avoid legal liability, although not general legal advice. The Borough did not violate the Open Meetings Act.
2. TAXING AGENCY METHODOLOGY
The recognized standard of review of administrative decisions involving questions of law or fact requiring agency expertise is the reasonable basis test. North Star Alaska Housing Corp. v. Fairbanks North Star Borough, Board of Equalization, 778 P.2d 1140, 1144 n. 7 (Alaska 1989). This court has used this deferential standard before for reviews of tax assessments: “Taxing authorities are to be accorded broad discretion in deciding among recognized valuation methods.” Id. at 1143-44. If a reasonable basis for the taxing agency’s method exists, the taxpayer must show fraud or the “clear adoption of a fundamentally wrong principle of valuation.” Hoblit v. Greater Anchorage Area Borough, 473 P.2d 630, 632 (Alaska 1970) (quoting Twentieth Century Investment Co. v. City of Juneau, 359 P.2d 783, 788 (Alaska 1961)).24
b. The Parties’ Relative Burdens of Proof.
Alaska law provides that the taxpayer bears the burden of proof before a Board [1263]*1263of Equalization. “The only grounds for adjustment of the assessment are proof of unequal, excessive, improper, or under valuation based on the facts that are stated in a valid, written appeal or proven at the appeal hearing.” AS 29.45.210(b). The Borough Code contains similar language. FNSB 3.24.012(C)(2). The Borough contends throughout its brief that Cool Homes lost its appeal because it failed to offer adequate evidence, including suggestions as to what the proper valuation method should be. Cool Homes counters that it should prevail because the Borough must justify its valuation method and demonstrate that it is supported by substantial evidence.
taxpayer contesting an assess-assessneed only prove that the valuation is improper. The taxpayer does not have to offer the correct amount, range or method of valuation, as the Borough repeatedly insisted. See Alascom, Inc. v. North Slope Borough Bd. of Equalization, 659 P.2d 1175, 1180 (Alaska 1983) (noting that the Borough has responsibility of making valid assessment); North Star Alaska Housing, 778 P.2d at 1146 (stating that the proper remedy is to remand to the Board for redetermination). The burden then shifts to the taxing authority to introduce credible evidence which substantiates its assessment. See Hoblit, 473 P.2d at 632.25
However, AS 29.45.210(b) still requires that the taxpayer prove facts at the hearing. Moreover, the Borough Code states that the “Appellant’s presentation must contain evidence which, if not contradicted, would prove an unequal, excessive, improper or under valuation.” FNSB 3.24.-012(C)(2). It is not enough merely to argue that the valuation was inadequate or demand a justification from the taxing authority.
c. Adjustment for Lease Restrictions.
The Borough employed a valuation method whereby the land subject to Cool Homes’ leasehold was valued as a fee simple interest and then adjusted to reflect the leasehold’s restrictions and the reversion-ary interest of the United States. The Borough used a 10 percent adjustment factor to reflect the restrictions. This method and the 10 percent factor have been approved by this court before for a similar lease and housing project on United States military lands. North Star Alaska Housing, 778 P.2d at 1145-46.
Cool Homes contends that 10 percent does not adequately reflect the extensive restrictions on its leasehold.26 It argues that the Borough has never put forward evidence to demonstrate that a 10 percent factor accurately reflects the differences [1264]*1264between the value of Cool Homes’ leasehold interest and the hypothetical fee simple value. Thus, the Board had no reasonable basis upon which to affirm the assessment.
Moreover, Cool Homes contends that it has met its burden of proving that the 10 percent adjustment is unsound. The thrust of its argument is that because of recognized differences27 between Cool Homes’ interest and the interest in North Star Alaska Housing and other projects in Fairbanks, the same 10 percent factor should not have been used.
The evidence before the Board that the lease restrictions were improperly accounted for consisted of the affidavit of Kenneth D. Lougee, counsel for Ben Lomond, Inc., which was filed with the Board in 1986; the deposition and testimony of Mr. Norm Thompson, president of Cool Homes, presented in the 1987 hearing; and Mr. Loug-ee’s argument before the Board in 1987. Mr. Lougee’s affidavit merely stated that both the Cool Homes property and the Railroad Industrial Area property in Fairbanks were assessed the same 10 percent deduction, even though the Railroad property is not located on a federal enclave. Thompson’s deposition detailed the lease restrictions in Cool Homes’ contract with the Air Force. Mr. Lougee’s testimony noted that Cool Homes’ interest was distinguishable from that of the North Star project because the land lease outlasted the project lease.
The evidence produced by Cool Homes is insufficient to satisfy its burden, thereby triggering the Borough’s burden to defend the 10 percent deduction. All Cool Homes has said is that its leasehold had many restrictions and that it was different than other properties for which the 10 percent adjustment was also used. It offered minimal evidence that the 10 percent was “unequal, excessive or improper” and did not reflect these restrictions. The Board thus had a reasonable basis for affirming the assessment with respect to the adjustment for lease restrictions.
d. Salvage Value.
The Board of Equalization upheld and assessed improvements valuations for Cool Homes’ interest in the sum of $24,-527,500 for 1987, $22,633,512 for 1988, and $21,690,449 for 1989. These valuations were arrived at by a replacement cost method. Under this method the current replacement cost of the improvements was calculated using two alternative cost formulas. The assessor used the lower result. This was then reduced by a factor of 15 percent to account for presumed savings because of the size of the Cool Homes’ project. The resulting figure was in turn depreciated at the rate of four percent per year over 20 years with 1987 used as the base year. Thus, the Borough assumed that Cool Homes’ interest in the improvements would lose 80 percent of its value over the term of the lease. The remaining 20 percent was attributed to salvage value, [1265]*1265that is, the value from the improvements which Cool Homes could recover at the end of the lease.
Borough assessment personnel crosschecked the result reached by the replacement value approach by referring to market indicators and a capitalization of income approach. Testimony indicated that the best market indicator was the fact that Aetna Life Insurance Company had loaned Cool Homes’ predecessor $30,000,000 as permanent financing for the project. Borough assessment personnel testified that if a market approach had been used “we would have come in with somewhere around $30,000,000” based on this transaction. Based on the income stream calculation, Borough personnel testified that a valuation of roughly $28,000,000 would have been appropriate in the first year.28 Deputy Assessor McManus testified that the replacement cost method was employed rather than direct market comparisons or income capitalization because replacement cost is uniformly used throughout the Borough for all improved property.
Focusing on the replacement cost method employed by the Borough, Cool Homes contends that the use of any salvage value is inappropriate. It relies on the following finding made by Superior Court Judge James R. Blair in a prior appeal:
After the twenty-year term is up, the lease is renewable at the government’s option. If the government opts not to renew the lease, Cool Homes’ sole recourse is to remove the buildings within thirty days and restore the land to its prior condition. It is undisputed that the buildings cannot be so removed.
The Borough defends the 20 percent salvage value by referring to testimony by Deputy Assessor McManus which suggests that the buildings can be moved29 and that in any event even if they had to be dismantled on site, a 20 percent salvage value figure would be appropriate. McManus stated:
We’re saying that if entrepreneur or entrepreneurs or just people that wanted to buy things, if they’d be willing to pay 20$ on the dollar, they’d dismantle and cart them off, but more appropriately that they relocate them as units in place. Certainly there’s a cost and Ray Mark indicated the cost, it averaged around $8,500 to move the Hutchinson Career four-bedroom out to North Pole. And he said that price can vary depending upon how many electrical lines are in the way; how many obstacles; it’s a fairly clear shot from Eielson to, perhaps, the North Pole area; probably more clear than from out there off of University Avenue. But, basically, it appeared from the marketplace that individuals were willing to pay 50$ on the dollar for new ones. We also took a look at homes that were in the salvage value condition, and either need to be completely refurbished, or actually relocated elsewhere and — or, in some cases, dismantled and salvaged, the components of them, and any way that we looked at them we still came up with about a 20 percent value. So, we thought that the 20 percent was fair over a 20-year period.30
At another point McManus further explained the salvage figure:
And at the end of that 20 years one of the options available is that Cool Homes [1266]*1266will remove improvements from the Eiel-son Air Force Base land and that’s where the 20 percent salvage comes in. To determine that 20 percent we took a look at Hutchinson Career Center who has been building, for several years now, homes that they do build, but they’re sitting on — they’re sitting to be relocated. And those prices have ranged from $25,001 all the way up to $52,000 depending on the magnitude of the size, I should say, of the structure. They’re the same structures, once placed on a tract of land, full site improvements, on foundation, with water and sewer, generating a value of — The lowest was $51,000, the highest was $96,000. And we rounded this to conclude that it was .50$ on the dollar that individuals were willing to pay for a structure that had to be relocated. We checked with Ray Mark with Mark Acres to find out the cost of relocating these structures and in our mind was that people could safely invest 50$ on the dollar. But, we’re looking at a rather large project here so we had to deduct the 20 percent from there and that’s where we come up with the 40$ on the dollar for their improvements recognizing that these would be 20 years old on a four [sic forty] year economic life is the same as saying that we’d reduce it from 40$ to 20$ then, or half used up. And the 20$ on the dollar then we felt was a fair estimate of salvage value and that equates to 20 percent.
Although there was evidence presented by Cool Homes that the structures could not be relocated, the testimony of Mc-Manus, especially as it relates to the buildings’ value in a dismantled state, is sufficient, in our view, to substantiate the assessment.
As a part of its argument that the Borough erred in using a 20 percent salvage value, Cool Homes states: “The use of a salvage value in connection with ‘accelerated depreciation,’ is also erroneous.” Cool Homes’ argument seems to be that depreciating the improvements over a 20-year life fails to consider the residual value to the government of the improvements since the useful life of the buildings is at least 40 years.
This argument lacks merit. The Borough depreciated the improvement over 20 years rather than 40 because in an earlier appeal of this case to the superior court the superior court accepted Cool Homes’ predecessor’s argument that assessing its interest based on a 40-year useful life did not take into account the fact that there was only a 20-year lease. See Ben Lomond, Inc. v. Board of Equalization, 760 P.2d 508, 510 (Alaska 1988). To contend that the 20-year depreciation schedule does not account for the government’s reversionary interest is clearly wrong. Because of the accelerated depreciation, Cool Homes will be taxed in future years on a value which is progressively less than the replacement cost of the project taken as a whole. The difference between the amount on which Cool Homes is taxed and the replacement cost, less depreciation keyed to the true useful life of the buildings, is the reversion-ary interest to the government.
3. CROSS-APPEAL: SUPPLEMENTATION OF THE RECORD BY THE SUPERIOR COURT
In May, 1989 the Board of Equalization affirmed the Borough’s tax assessment of Cool Homes’ real property interests. In June, Cool Homes appealed to the superior court. During the course of the appeal, Cool Homes noticed that a document entitled “Assignment of Rents and Leases” was not part of the record. On May 16, 1990, it filed a Motion to Supplement Record. The motion was granted by order of the superior court in October. The Borough appeals, contending that the motion to supplement was improperly granted.
A board of equalization is authorized in the Municipal Government title of the Alaska Statutes. AS 29.45.200. A determination of a board of equalization may be [1267]*1267appealed to the superior court “as provided by the rules of court applicable to appeals from decisions of administrative agencies.” AS 29.45.210(d). The superior court hears the appeals “on the record established at the hearing before the board of equalization.” AS 29.45.210(d).
The limitation on the record was added to the provision in 1985. The section which was replaced, former AS 29.53.-140(f), allowed for trial de novo on appeal to the superior court. The legislature thus expressly chose to limit the scope of review of the board’s determinations. See Winegardner v. Greater Anchorage Area Borough, 534 P.2d 541, 547 (Alaska 1975) (noting that a trial de novo allowed by former statute on issue of whether assessment was proper “represents a decision by the legislature that in tax assessments, the borough assembly shall not be the only judge in its own case”). This is in contrast to the statute governing the appeal to the superior court of some state administrative agencies. AS 44.62.570(d).31
However, supplementation of the record has not prejudiced the Borough. Even with the supplemented record, the superior court ruled in the Borough’s favor. The supplemented document does not impact this court’s decision because it has not been argued in Cool Homes’ briefs before this court. Thus, the granting of the motion was harmless error which this court will disregard. See Boyles v. Smith, 759 P.2d 518, 521 (Alaska 1988).
III. CONCLUSION
The court’s grant of summary judgment in S-3995, the Borough’s action to foreclose Cool Homes’ interest in its buildings on Eielson Air Force Base, is REVERSED and REMANDED for further proceedings consistent with this opinion. The court’s grant of summary judgment in S-4337 for personal judgment to recover property tax assessed against Cool Homes’ leasehold interest is AFFIRMED.
Concerning Nos. S-4338/4353 the Board did not violate the Open Meetings Act by conferring in private with its attorney before hearing Cool Homes’ case. With respect to the validity of the tax assessment of Cool Homes’ property, the Board did have a reasonable basis for affirming the Borough’s assessment which included a salvage value and accelerated depreciation. The Board had a reasonable basis to affirm the use of the 10 percent factor to reflect lease restrictions.
The superior court’s grant of summary judgment is REVERSED and REMANDED for further proceedings consistent with this opinion.